What is segmental duplication genetics?
Segmental Duplications (SDs) are long DNA sequences (typically defined as being > 1kb in length) that have nearly identical sequences (90-100%) and exist in multiple locations as a result of duplication events. SDs can be tandem or interspersed, and can be interchromosomal or intrachromosomal.
What are large segment duplications?
Segmental duplications are duplicated blocks of genomic DNA typically ranging in size from 1–200 kb (IHGSC 2001). They often contain sequence features such as high-copy repeats and gene sequences with intron–exon structure.
What is segmental duplications in human genome?
Segmental duplications (also termed “low-copy repeats”) are blocks of DNA that range from 1 to 400 kb in length, occur at more than one site within the genome, and typically share a high level of (>90%) sequence identity (reviewed by Eichler [2001]).
How common are segmental duplications?
Segmental Duplications. Approximately 5.2% of the human genome consists of segmental duplications or “duplicons”; ie, regions of more than 1 kb with >90% identified that are present more than once in the genome.
What is segmental deletion?
Chromosomal segmental deletion is a frequent cause of human disease. Such chromosomal microdeletion regions span a few Mb genomic DNA sequences and contain multiple genes. Deletion of multiple genes often leads to haploinsufficiency syndromes.
What causes gene duplications?
Gene duplications can arise as products of several types of errors in DNA replication and repair machinery as well as through fortuitous capture by selfish genetic elements. Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage.
Why are gene duplications relevant in the context of evolution?
Gene and genome duplications provide a source of genetic material for mutation, drift, and selection to act upon, making new evolutionary opportunities possible. As a result, many have argued that genome duplication is a dominant factor in the evolution of complexity and diversity.
For which organisms have whole-genome duplications been significant in their evolutionary histories?
Based on whole-genome analysis of Arabidopsis thaliana, there is compelling evidence that angiosperms underwent two whole-genome duplication events early during their evolutionary history.
What would be a likely explanation for the existence of pseudogenes?
Pseudogenes originate from decay of genes that originated from duplication through evolution. The decays include point mutations, insertions, deletions, misplaced stop codons, or frameshifts of a gene. The decay may occur during duplication, and these disablements may cause loss of a gene function.
How can duplications arise?
Duplications arise from an event termed unequal crossing-over that occurs during meiosis between misaligned homologous chromosomes. The chance of it happening is a function of the degree of sharing of repetitive elements between two chromosomes.
What is genome expansion?
Genome size expansion results in more severe ratchet effects, with a marked increase in the rate of mutations reaching fixation in the regions of the genome that are under weaker selection, alongside a moderate increase in core genome mutation fixation rate (Figure 6).
What are segmentsegmental duplications?
Segmental duplications (SDs) are DNA fragments with near-identical sequences that are greater than 1Kb [ 1 ]. They have been recognized as important mediators of gene and genome evolution, and are considered the origins for gene gain, functional diversification, and gene family expansion [ 1, 2 ].
What are core and segmental duplicons?
Core duplicons are segments of DNA that are duplicated and dispersed only within the genome of hominins and great apes. 32 They are also referred to as segmental duplications. Core duplicons move throughout the genome and can randomly carry neighboring pieces of DNA with them (Fig. 1.14 ).
Are there large-scale segmental duplications in the thaliana genome?
The complete sequencing of the A. thaliana genome revealed numerous large-scale segmental duplications [ 1, 6 – 10 ].
What is the distribution of gene family size and duplication?
Distributions of gene family sizes and patterns of duplication by genomic distance are also described in order to characterize patterns of local duplication and copy number for large gene families. Both gene family size and duplication by distance closely follow power-law distributions.